Method for preparing a catalyst for partial oxidation of acrolene

ABSTRACT

The present invention provides a method for producing a catalyst comprising an inert carrier an a mixed metal oxide as a catalytically active component supported on the inert carrier, the method comprising the steps of: a) adding organic acid(s) into solvent(s) and salt of each metal component which will form a mixed metal oxide, to prepare a catalyst precursor solution for the mixed metal oxide; b) adjusting pH of the catalyst precursor solution using a basic solution; c) containing the catalyst precursor solution for the mixed metal oxide, of which the pH is adjusted, on the inert carrier, d) removing the solvent(s); and e) calcining the resultant from step d. The catalyst produced by the present method has improved reproducibility, activity and yield, while maintaining a high selectivity.

TECHNICAL FIELD

The present invention relates to a catalyst for vapor phase partialoxidation comprising an inert carrier and a mixed metal oxide as acatalytically active component supported on the inert carrier; to amethod for preparing the same; and to a method for preparing a partiallyoxidized organic compound by use of the catalyst.

BACKGROUND ART

A catalyst comprising a mixed metal oxide is useful for vapor phasepartial oxidation of alkane, alkene or a mixture of alkane and alkene toan unsaturated carboxylic acid and for vapor phase oxidation of alkane,alkene or a mixture of alkane and alkene to unsaturated nitrile in thepresence of ammonia.

For the production of acrylic acid, it has been widely practiced on acommercial scale a method which adopts acrolein as a raw material andaffects the vapor phase partial oxidation thereof with molecular oxygenin the presence of a catalyst. Some patent applications disclosing acatalyst used for the production of the acrylic acid through the vaporphase oxidation of acrolein have been filed. The acrolein oxidationcatalyst disclosed in the applications comprises molybdenum and vanadiumas main components, and components, such as tungsten, chrome, copper,potassium and the like, are added, thereby improving capability thereof.For example, Japanese Patent Publication No. 12129/69 discloses acatalyst consisting of molybdenum, vanadium and tungsten, JapanesePatent Publication No. 25914/75 discloses a catalyst consisting ofmolybdenum, vanadium, copper and chrome, and Japanese Unexamined PatentPublication No. 85091/77 discloses a catalyst consisting of molybdenum,vanadium, copper, and at least one component selected from antimony andgermanium. In addition, European Patent No. EP-023859 discloses thatalthough the components and composition of the catalyst are identical,the conversion rate of the acrolein and a yield of the acrylic acid aresignificantly varied depending upon a method of forming the catalyst,when producing the catalyst. Also, the above European Patent discloses amethod for producing the catalyst which produces acrylic acid at yieldsof high levels.

Recently, a demand for the catalyst having more high conversion rate andyield is increased. Studies for producing the corresponding catalyst areactively proceeding.

For example, when the catalyst for partially oxidizing the acrolein tothe acrylic acid comprising the mixed metal oxide is prepared, it isdifficult to uniformly maintain a suspension, since the precipitate isgenerated by reaction of a cationic metal salt with anionic metal saltin an aqueous solution, is rapidly settled when agitation is stopped andthus is phase separated from a water layer.

When containing on the inert carrier the suspension with the phaseseparation, it is difficult to maintain the uniformity, causing theuniformity problem of a catalyst article whenever the catalyst isproduced. Also, if a particle size of a precipitate is large, it isdifficult to transfer the suspension through a pumping operation and tocontain the catalyst on the carrier using nozzle injection, so that theproduction thereof may run into a snag. In addition, the capacity of thecatalyst is remarkably dependent upon the particle size of the metalsalt contained in the suspension. Preferably, these metal salts consistof particles of less than 10 microns (refer to Korean Patent PublicationNo. 1998-073604). Accordingly, it is required to have a method ofeffectively suppressing the layer separation and decreasing the particlesize of the suspension.

DISCLOSURE OF THE INVENTION

The present invention accomplishes the above demand by treating theprecursor suspension for a mixed metal oxide with organic acid(s).

An object of the present invention is to provide a catalyst for vaporphase partial oxidation comprising an inert carrier and a mixed metaloxide as a catalytically active component supported on the inertcarrier; to a method for preparing the same; and to a method forpreparing a partially oxidized organic compound by use of said catalyst.

In order to accomplish the above mentioned objects, there is provided amethod for producing a catalyst comprising an inert carrier and a mixedmetal oxide as a catalytically active component supported on the inertcarrier, the method comprising the steps of:

-   -   a) adding organic acid(s) into solvent(s) and salt of each metal        component which will form said mixed metal oxide, to prepare a        catalyst precursor solution for the mixed metal oxide;    -   b) adjusting pH of the catalyst precursor solution using a basic        solution;    -   c) containing the catalyst precursor solution for the mixed        metal oxide, of which the pH is adjusted, on the inert carrier;    -   d) removing the solvent(s); and    -   e) calcining the resultant from step d.

According to another aspect of the present invention, there are provideda catalyst produced according to the above method; a method forproducing an unsaturated carboxylic acid by vapor phase partialoxidation of alkane, alkene or a mixture of alkane and alkene inpresence of said catalyst; and a method for producing an unsaturatednitrile by vapor phase partial oxidation of alkane, alkene or a mixtureof alkane and alkene with ammonia in the presence of said catalyst.

The mixed metal oxide used as a catalytically active component in thecatalyst for vapor phase partial oxidation is represented by thefollowing formula 1, and said catalyst can be used for production ofacrylic acid by oxidation of acrolein.Mo_(a)W_(b)V_(c)A_(d)B_(c)O_(x)   Formula 1wherein, Mo is molybdenum, W is tungsten, V is vanadium, O is oxygen, Ais at least one element selected from a group consisting of iron,copper, bismuth, chrome, tin, antimony and potassium; and B is at leastone element selected from a group consisting of alkali earth metals; a,b, c, d and e denote the atom ratio of the respective metals,respectively, provided that, in the case that a is 12, b is 1 to 5, c is1 to 6, d is 1 to 5, e is 0 to 3, and x is a value determined dependingupon oxidizing state(s) of other elements.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the present invention as claimed.

BEST MODE FOR CARRYING OUT THE INVENTION

A method for producing a catalyst for partial oxidization comprising amixed metal oxide will now be described in detail with reference topreferred embodiments of the present invention.

The present invention provides to the method for producing a catalystfor vapor phase partial oxidation comprising an inert carrier and amixed metal oxide as a catalytically active component supported on theinert carrier, characterized by treating organic acid(s) when preparinga catalyst precursor suspension for the mixed metal oxides.

The organic acid is reacted with the metal salt, thereby producing achelate compound. Since the produced chelate compound is easily solublein water, precipitation of metal generated when producing metal oxidecatalyst using a precipitating method may be prevented, and smallercatalyst particle may be produced. In addition, it is important toadjust the proper level of pH so as to improve the capability of thecatalyst. In the case that the pH is not at the proper level, it wasfound that the capability of the catalyst is abruptly decreased.

The catalyst for vapor phase partial oxidation comprising the inertcarrier and the mixed metal oxide as the catalytically active componentsupported on the inert carrier according to the present invention can beprepared in accordance with the method known in the art, except that theprecursor solution treated by the organic acid is used. Specifically,the composition of catalyst, the method for production thereof, the kindof carrier, and the method for containing a catalyst component on thecarrier may be each any of those known in the art.

The catalyst precursor solution for the mixed metal oxide ascatalytically active component according to the present invention may beproduced by mixing at least one solvent and metal salts in appropriateamounts to form the mixed metal oxide as catalytically active component,wherein the catalyst precursor solution may be a slurry, a dispersion, asolution or combination thereof. The solution is preferable. Solvent isthen removed, and the precursor mixture is calcined.

An atomic ratio of the respective metal components in the solution,dispersion or slurry is previously determined to be a metal ratio of themixed metal oxide catalyst component to be produced.

Suitable solvents for the precursor solution include water; alcoholsincluding, but not limited to, methanol, ethanol, propanol, and diols,etc.; and other polar solvents known in the art. Generally, water ispreferred. The water includes, without limitation, distilled water anddeionized water. An amount of the water is preferably determined as anamount sufficient to keep the components substantially in solutionenough to avoid or minimize compositional and/or phase separation duringthe production steps. Accordingly, the amount of water will varydepending upon the amounts and solubilities of the materials to becombined. Though lower amount of water are possible for forming theslurry, as described above, the amount of water is preferably sufficientto ensure that an aqueous solution is formed at the time of mixing.

In the method for producing the mixed metal oxide as catalyticallyactive component, the metal compounds may be used in state(s) selectedfrom ammonium salts, nitrates, various oxides, carbonates, chlorides,sulfates, hydroxides, organic acid salts, and the like.

In order to produce the chelate compound using the metal salt and theorganic acid at the production of the precursor solution for the mixedmetal oxide as catalytically active component, the amount of organicacid to be added should be adjusted, and the amount of added organicacid should be properly adjusted depending upon the total moles ofmolybdate of the metal salt.

To establish the effect of the acid-treatment, the amount of organicacid added in the production of the catalyst is in a mole ratio of 0.5to 5, preferably 0.8 to 3.0, on the base of the molybdate. The pH of theprecursor solution provided to maintain the capability of the catalystis maintained in a range of 4 to 6 by use of base substance such asammonia, pyridine, etc.

In the case of the precursor solution produced according to the presentinvention as described above, less than particle size of metal salt canbe obtained, and the problem of phase separation of the precursorsolution can be solved.

Preferably, the organic acid is a C₁˜C₁₀ organic acid comprising atleast one of hydroxyl and carboxyl group. The organic acid usable in thepresent invention comprises citric acid, maleic acid, oxalic acid andthe like, which is not limited thereto.

The inert carrier to be used in the present invention does not need tolimit the material therefor.

The carrier, which can be used in producing the oxidizing catalyst forthe production of the acrylic acid by the vapor phase partial oxidationof acrolein or an acrolein-containing gas, can use any of materialswhich are widely known as usable for the production. As examples of thematerial widely used for the carrier of the catalyst, it may be citedalumina, silica, silica-alumina, titania, magnesia, silica-magnesia,silica-magnesia-alumina, silicon carbide, silicon nitride, and zeolite,and preferably silica-alumina, silica-magnesia-alumina, silicon carbideor the like.

The carrier is not particularly limited on account of physicalproperties, shape, size etc. As respects the physical properties of thecarrier, the specific surface area thereof is not more than 2 m²/g,preferably in the range of 0.01 to 1.5 m²/g, the water absorption ratiothereof is in the range of 0 to 70%, preferably 0 to 50%, and theaverage pore diameter thereof is in the range of 1 to 1,500 μm,preferably 5 to 500 μm. The shape of the carrier may be arbitrarilyselected from sphere, cylinder, hollow cylinder and the like. The sizeis in the range of 1 to 10 mm, preferably 3 to 8 mm, in diameter in thecase of spheres.

The amount of the catalytic component to be contained on the carrier isnot particularly limited but is only required to be such that theproduced catalyst permits effective production of acrylic acid by thevapor phase partial oxidation of acrolein. This amount, for example, isin the range of 1 to 200 wt. %, preferably 10 to 100 wt. %, based on theweight of the carrier for producing the acrylic acid.

The catalyst precursor solution treated by the organic acid according tothe present invention is easily pumped and transferred, and can beinjected through a nozzle, so that steps of containing the precursorsolution for the mixed metal oxide on the inert carrier may beeffectively performed. In addition, the present invention can solve theproblem of the uniformity of article due to the layer separation, and aless than size of the metal salt can be obtained, thereby remarkablyimproving the capability of the catalyst.

Once the catalyst precursor solution treated by the organic acidaccording to the present invention is contained on the carrier, theliquid therein is removed by any suitable method known in the art. Suchmethods include vacuum drying, freeze drying, spray drying, rotaryevaporation and air-drying, which it is not limited thereto. Vacuumdrying is generally performed at pressure ranging from 10 mmHg to 500mmHg. Freeze drying typically entails freezing the slurry, dispersion orsolution, using, for instance, liquid nitrogen, and drying the frozenslurry, dispersion or solution under vacuum. Spray drying is generallyperformed under an inert atmosphere such as nitrogen or argon, with aninlet temperature ranging from 125° C. to 200° C. and an outlettemperature ranging from 75° C. to 150° C. Rotary evaporation isgenerally performed at a bath temperature of from 25° C. to 90° C. andat a pressure of from 10 mmHg to 760 mmHg, preferably at a bathtemperature of from 40° C. to 90° C. and at a pressure of from 10 mmHgto 350 mmHg, more preferably at a bath temperature of from 40° C. to 60°C. and at a pressure of from 10 mmHg to 40 mmHg. Air drying may beeffected at a temperature ranging from 25° C. to 90° C. The rotaryevaporation or air-drying is generally preferred.

The catalyst precursor resulting from the drying is calcined. Thecalcination may be conducted in an oxygen-containing atmosphere or in anatmosphere free of oxygen (e.g., an inert atmosphere or vacuum). Theinert atmosphere may be any material which is substantially inert, i.e.,does not react or interact with the catalyst precursor. A suitableexample includes, but it is not limited to, nitrogen, argon, xenon,helium or a mixture thereof. Preferably, the inert atmosphere is argonor nitrogen. The inert atmosphere may flow over the surface of thecatalyst precursor or may not flow thereover (a static environment).When the inert atmosphere does flow over the surface of the catalystprecursor, the flow rate can vary over a wide range, e.g., at a spacevelocity of from 1 to 500 hr⁻¹.

The calcination is usually performed at a temperature of from 350° C. to850° C., preferably from 400° C. to 700° C., more preferably from 500°C. to 640° C. The calcination is performed for an amount of timesuitable to form the aforementioned catalyst. Typically, the calcinationis performed for from 0.5 to 30 hours, preferably for from 1 to 25hours, more preferably for from 1 to 15 hours, to obtain the mixed metaloxide uniformly supported on the carrier.

As an example of the partially oxidized organic compound to be obtainedby the use of the vapor phase partial oxidation catalyst according tothe present invention, it may be cited an unsaturated aldehyde or anunsaturated carboxylic acid having not less than three carbon atoms andan organic acid anhydride or a nitrile compounds having not less thanfour carbon atoms. The unsaturated aldehyde or unsaturated carboxylicacid includes those having three to five carbon atoms, more preferably(meta)acrolein and (meta)acrylic acid. The organic acid anhydride ornitrile compound includes aromatic acid anhydride compounds, aromaticnitrile compounds and heterocyclic nitrile compounds, preferably organicacid anhydride, aromatic nitrile and heterocyclic nitrile having four toten carbon atoms, and more preferably phthalic anhydride, maleicanhydride, pyromellitic anhydride, benzonitrile, picolino-nitrile andthe like.

The method for producing the acrylic acid by the vapor phase partialoxidation of acrolein or an acrolein-containing gas in the presence ofthe catalyst according to the present invention has no particularrestriction. It can be effected by any of the methods which can be usedfor reactions of this kind and which are widely known as usabletherefor. The present invention can adopt any reaction conditions knownto be available in producing acrylic acid at a fixed-bed multi-tubereactor. The production, for example, only requires acrolein or anacrolein-containing gas to contact with the catalyst at a temperature inthe range of 180° C. to 350° C., preferably 200° C. to 330° C., under anormal pressure state or a pressurized state.

The present invention will now be described in detail with reference tothe below embodiments and experiments. The embodiments are intended tobe illustrative only, and the present invention is not limited thereto.

Production of Catalyst

EMBODIMENT 1

400 ml of distilled water was filled in a glass reactor having a volumeof 500 cc and was agitated, while it was heated to a temperature of 97°C. 50 g of citric acid was solved thereto, and then 100 g of ammoniummolybdate, 19.71 g of ammonium paratungsten and 22.09 g of ammoniummetavanadate were solved. After the temperature of the resultingsolution was lowered to 75° C., 21.67 g of copper nitrate and 6.29 g ofstrontium nitrate were inputted into the solution in turn to produce asuspension. The pH of the produced suspension was adjusted to 5.0 by useof an ammonium water.

The resulting suspension was contained on an inert carrier through aspray nozzle, and was coated on the carrier by drying it using a hotblast of 90° C. Such catalyst coated on the carrier was dried at atemperature of 120° C., and then was calcined at a temperature of 400°C. for hours, with air flowing thereon, thereby producing the catalyst.At that time, the coated catalyst powders after the calcination were 25wt %. The element composition of the produced catalyst components exceptfor oxygen was Mo₁₂W_(1.6)V₄Cu_(1.9)Sr_(0.63).

EMBODIMENT 2

A catalyst was produced in the same manner as used in Embodiment 1,except for that 100 g of citric acid is solved and the pH of thesuspension is adjusted to 4.5 with ammonia water.

EMBODIMENT 3

A catalyst was produced in the same manner as used in Embodiment 1,except for that 100 g of citric acid is solved and the pH of thesuspension is adjusted to 5.5 with ammonia water.

EMBODIMENT 4

A catalyst was produced in the same manner as used in Embodiment 1,except for that 60 g of oleic acid is solved instead of the citric acid.

EMBODIMENT 5

A catalyst was produced in the same manner as used in Embodiment 1,except for that 50 g of maleic acid is solved instead of the citricacid.

COMPARATIVE EMBODIMENT

b 400 ml of distilled water was filled in a glass reactor having avolume of 500 cc and was agitated, while it was heated to a temperatureof 97° C. 100 g of ammonium molybdate, 19.71 g of ammonium paratungstenand 22.09 g of ammonium metavanadate were solved thereto. After thetemperature of the resulting solution was lowered to 75° C., 21.67 g ofcopper nitrate and 6.29 g of strontium nitrate were inputted into thesolution in turn to produce a suspension.

The resulting suspension was contained on an inert carrier through aspray nozzle, and was coated on the carrier by drying it using a hotblast of 90° C. Such catalyst coated on the carrier was dried at atemperature of 120° C., and then was calcined at a temperature of 400°C. for 5 hours, with air flowing thereon, thereby producing thecatalyst. At that time, the coated catalyst powders after thecalcination were 25 wt %. Element composition of the produced catalystcomponents excepting oxygen was Mo₁₂W_(1.6)V₄Cu_(1.9)Sr_(0.63).

Example of Test

Catalyst Activating Test

The catalysts produced by the embodiments were filled in the reactor,and oxidation of acrolein was performed to produce acrylic acid.Reaction conditions for producing the acrylic acid are following:temperature of the reactor is 250° C. to 300° C.; pressure of thereactor is 1 to 3 atmospheric pressure; and raw gas of mixed gas, ofwhich a volume ratio of acrolein:oxygen:vapor:nitrogen is7.0:5.6:15:72.4, is introduced on the catalyst in 500 to 2000 hours ofspace velocity(STP). Results of the reaction tests on the embodimentsand the comparative embodiment are shown in Table 1.

In the methods known in the art, as well as the conventional methoddescribed hereinbefore, it was reported that a conversion rate of theacrolein is more than 80%, a selectivity of the acrylic acid is 85% to99%, and a yield of the acrylic acid is 77% to 98%. However, sinceconditions for testing the capability of the catalyst are various, it isinsignificant to compare the above results with values disclosed inprior documents.

In the embodiments, the conversion rate of the acrolein and the yield ofthe acrylic acid are calculated according to the following Equations 1and 2.Conversion rate (%) of acrolein=[mole of reacted acrolein/mole ofsupplied acrolein]×100   Equation 1Yield (%)=[mole of produced acrylic acid/mole of supplied acrolein]=100  Equation 2 TABLE 1 Conversion Reacting Rate of Yield of Catalyst Temp.Acrolein Acrylic Embodiment Organic Acid Composition (° C.) (%) Acid (%)1 Citric Acid Mo₁₂W_(1.6)V₄Cu_(1.9)Sr_(0.63) 270 99.32 89.75 2 CitricAcid Mo₁₂W_(1.6)V₄Cu_(1.9)Sr_(0.63) 270 99.21 89.55 3 Citric AcidMo₁₂W_(1.6)V₄Cu_(1.9)Sr_(0.63) 270 99.12 89.35 4 Maleic AcidMo₁₂W_(1.6)V₄Cu_(1.9)Sr_(0.63) 270 98.52 88.12 5 Oleic AcidMo₁₂W_(1.6)V₄Cu_(1.9)Sr_(0.63) 270 98.10 87.43 Comparative —Mo₁₂W_(1.6)V₄Cu_(1.9)Sr_(0.63) 270 95.21 84.23

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers allmodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

Industrial Applicability

On the base of the test results of acid treating the catalyst precursorsolution using various organic acids in the production of catalyst, itcan be appreciated that the present invention can provide a catalystwith improved reproducibility, activity and yield, while maintaining ahigh selectivity relative to the acrylic acid.

1. A method for producing a catalyst comprising an inert carrier and amixed metal oxide as a catalytically active component supported on theinert carrier, the method comprising the steps of: a) adding organicacid(s) into solvent(s) and salt of each metal component which will forma mixed metal oxide, to prepare a catalyst precursor solution for themixed metal oxide; b) adjusting pH of the catalyst precursor solutionusing a basic solution; c) containing the catalyst precursor solutionfor the mixed metal oxide, of which the pH is adjusted, on the inertcarrier; d) removing the solvent(s); and e) calcining the resultant fromstep d.
 2. The method as claimed in claim 1, wherein the mixed metaloxide used as a catalytically active component in the catalyst for vaporphase partial oxidation is represented by the following formula 1, andwherein the catalyst can be used for production of acrylic acid byoxidation of acrolein.Mo_(a)W_(b)V_(c)A_(d)B_(e)O_(x)   Formula 1 wherein, Mo is molybdenum, Wis tungsten, V is vanadium, O is oxygen, A is at least one elementselected from a group consisting of iron, copper, bismuth, chrome, tin,antimony and potassium, and B is at least one element selected from agroup consisting of alkali earth metals; a, b, c, d and e denote atomratio of the respective metals, respectively, provided that in case thata is 12 b is 1 to 5, c is 1 to 6, d is 1 to 5, e is 0 to 3, and x is avalue determined depending upon oxidizing states of other elements. 3.The method as claimed in claim 1, wherein carbon atomicity of theorganic acid is 1 to
 10. 4. The method as claimed in claim 1, whereinthe organic acid comprises at least one of hydroxyl and carboxyl group.5. The method as claimed in claim 1, wherein the organic acid isselected from a group consisting of citric acid, maleic acid and oxalicacid.
 6. The method as claimed in claim 1, wherein the organic acid isadded in a mole ratio of 0.5 to 5 on basis of molybdate.
 7. The methodas claimed in claim 1, wherein in step b, the pH of the precursorsolution is adjusted in a range of 4 to
 6. 8. The method as claimed inclaim 1, wherein in the step b, the basic solution is ammonia orpyridine.
 9. A catalyst for vapor phase partial oxidation comprising aninert carrier and a mixed metal oxide as a catalytically activecomponent supported on the inert carrier, produced according to any oneof claims 1 to
 8. 10. A method for producing an unsaturated carboxylicacid by vapor phase partial oxidation of alkane, alkene or a mixture ofalkane and alkene in the presence of the catalyst according to claim 9.11. A method for producing an unsaturated nitrite by vapor phaseoxidation of alkane, alkene or a mixture of alkane and alkene withammonia in presence of the catalyst according to claim 9.